Radiating gas burner



Feb. 20, 1962 Q HNGER 3,021,893

RADIATING GAS- BURNER Filed Nov. 8, 1954 FG'I' 4 a FIGS INVENTOR GUIDO HNGER am www ATTO RN EY tats lit iinite @iii Patented Fels. 20, 1962 3,021,893 RADilATlNG GA BURNER Guido Hnger, Zuchwil-Soiothurn, Switzeriand, assigner to Schweiz Gasapparateahrik Solothurn, Solothurn, Switzerland Filed Nov. 3, 1954, Ser. No. 457525 l Gaim. (Cl. 158-116) This invention relates to a radiating gas burn-er, of the type in which a gas pervious external diaphragm or delimitation is heated to incandescence by a gas-air-mixture flowing through and burning in close proximity of the said diaphragm.

Radiating or incandescent burners of that type are known. One type of such burners is provided with a gas pervious diaphragm in the form of a covering plate of chamotte, steatite or other refractory materials sintered to a homogeneous or to a coarse porous texture. rIhe thermal conductivity of many of such covering plates is much too high so that in radiating burners equipped with such plates the heat loss due to heat conduction from the incandescent surface to the interior of the burner was extremely high and the inner portions of the covering plates would be heated to such a degree that the com'- bustible mixture was ignited behind the covering plates in the mixing tube of the burner thereby causing a l'iash back of the dame to the gas nozzle.

in the endeavour to avoid the forementioned drawbacks and especially dash-back of the flame to the gas nozzle, highly porous plates having low heat conductivity have already been developed. But all of these known burners had also the common disadvantage that the mass of the covering plates was extremely high so that it took very long for the outer surface of the covering plate to reach incandescence. Besides an appreciable heat ow to the inner portions of the burner occurred in all of these covering plates in spite of relatively low heat conductivity of the material so that the eciency of such radiating burners was relatively poor.

It was also proposed to use limitations or diaphragms having an outer radiating layer, a thin anti-flash-back grid and a thick inner layer, whereby the anti-flash-back grid avoids flash back of the llame and too intensive heat exchange from the outer radiating layer to the thick inner layer. Since the thin anti-ash-back grid directly contacted the cooled inner layer and the incandescent outer layer, there was still an appreciable heat how from the outer radiating layer to the cooler interior so that the burner was rather sluggish in operation.

lt was further proposed to use a wire grid as an outer limitation of the burner and to provide another wire grid at an appreciable distance from the outer grid or two further grids at a distance from each other and from the said outer grid constituting the external limitation or diaphragm of the burner. lt was however found that this arrangement was not able to provide for stability against flash back of the flame to the mixing tube of the burner, because it was quite possible that the llame would ash back step by step from one grid to the other by overheating the grid over which the flame is burning and the gas-air-mixture immediately behind such grid so that the flame would flash back behind the grid and so on until the flame had reached the mixing tube of the burner. Therefore, the use of such burners wasl limited to certain operating positions wherein the dame would burn upwards or horizontally, but never downwards.

It is an object of this invention to provide a radiating burner which may be used in any position and of which the llame may burn in downward direction without any danger of flash back.

't is a further object of this invention to do away with all of the forementioned disadvantages of known radiating burners.

The radiating burner according to this invention is roadly characterized in that the said external diaphragm or deiirnitation of the burner has at least two gas pervious, gauze-like envelopes closely laid one upon another. These gas pervious envelopes may conveniently be made of sieve-like metal grids or nettings of any desired thickness and weight, whereby it is preferred to use two envelopes. It was found that the combustion takes place in the meshes of the outer of such envelopes and mmediately outside the envelope. Thereby the outer envelope is heated to red-hot incandescence whereas the inner envelope, only serving for preventing flash back of the dame, is relatively cool. A flash back of the combustion behind the outer envelope is prevented by the fact that the inner envelope is closely laid upon the outer envelope and is able to cool the combustible gas-air-mixture immediately behind lthe outer envelope. Thereby the gauze-like envelopes are laid one upon the other and no special care must be taken to keep them at a prescribed distance, whereby the heat conduction from the outer envelope to the inner envelope may appreciably be reduced. The inner envelope is further protected against overheating by the cooling action of the combustible mixture passing through it. This cooling action of the mixture behind the outermost envelope may be improved by the arrangement of more than two envelopes. lf wire grids or nettings are used they will contact each other in a few small areas only whereas they are at a small distance from each other in the major portion of their surface. Due to the sieve-like nature of the envelopes the heat radiated towards the interior of the burner may be reflected outwards through the meshes of the grids when a retiector is arranged behind the envelopes. Preferably the inner wall or" the burner head is made of a reflecting material such as aluminum or the like.

Other objects and advantages of the invention will be apparent from the following description and from the accompanying drawing in which:

FG. l is a cross-sectional view taken axially through a radiating burner in accordance with the present invention;

FIG. 2 is .an enlarged fragmentary plan View of the burner diaphragm formed of two juxtaposed wire nettin-gs, and

FIG. 3 is a cross-sectional view of the diaphragm taken on line 3-3 of FIG. 2.

Referring specically to FIG. l, the gas nozzle 1 of the burner is attached to a gas tube 3 by means of a screw 2 The gas willl flow through the axial bore 4 of the screw 2 to the gas nozzle l and flows into the mixing tube 5 which is slid onto the gas nozzle l and held thereon by means ofA a set screw. The mixing tube 5 has a lateral slit 6 for entry of the primary combustion air. A burner head having a distributing cap 7 and a cup like burner .body 8 with a reflecting inner wall is extensas screwed onto the thread provided at the lower end of the mixing tube 5. Two similar, sieve-like or gauze-like metal grids or wires nettings l constituting the outer diaphragm or delimitation of the burner, are attached to the laterally projecting flange of the burner body 8 by means of a pressing ring 9. These wire nettings 10, which include an outer netting 10a and an inner netting 10b, may be of any desired weight and thickness but the size of the meshes should not exceed l mm. if flash back shall be avoided in any case. Very good results are obtained when high refractory, corrosion-proof wire meshing is used for the envelopes of the outer burner diaphra'gm.

The radiating burner described and illustrated opreates as follows: The gas jet leaving the burner nozzle 1 aspirates air through the slit 6 and mixes with the same in the mixing tube of the burner. The combustible gasair-mixture leaves the mixing tube 5 through the holes in the burner cap 7 into the burner space between the wire nettings itl and the burner body 8. Thereupon the mixture llows through the wire nettings and burns in the meshes of the outer netting lila thereby heating the samet to incandescence. lf the oxygen contents of the mixture is not suicient for a complete combustion, the remaining combustible components of the mixture will be burnt, immediately outside the outer netting 10a which is heated to temperatures of 700 to 800 C. that is to red hot incandescence.

As already pointed out the combustion takes place in the meshes or in close proximity of the outer netting 10a whereby the netting is heated. ln order to obtain the desired radiation one single netting would be sullicient. It was found, however, that with such an arrangement the flame easily flashes back to the burner nozzle. According to this invention such an undesired flash back may conveniently and effectively be avoided by the arrangement of the inner wire netting 10b. The reasons why the flash back is prevented by the inner netting have been set out in the foregoing. The stabilisation of the burner has proved to be particularly effective when the nettings are so arranged that the wires of the one netting will overlie the mesh openings of the other netting, as shown in FiGS. 2 and 3.

With this staggered arrangement of the meshes of the nettings the outward radiation of the outer wire faces of the inner netting lill) through the mesh openings of the outer netting 10a is facilitated so that the radiation of the whole burner is improved and the inner netting 10b is cooled more effectively. The heat exchange from the incandescent outer netting 10a to the inner netting 10b is also rendered more dilllcult, so that flashing baci( of the burner is most effectively prevented by this arrangement.

The mass and consequently the heat capacity of the outer diaphragm or delimitation of the burner, consisting of the wire nettings itl, is very small and the above mentioned glowing temperature of the outer envelope lila is for instance reached within seconds in normal operation of the burner. In spite of the fact that the mass of the outer diaphragm lila is very small, the radiating face is relatively great because the heat radiated from the inner netting ltlb will radiate outwardly either directly or after reflection by the inner surface of the burner body 8.

The reflector or burner body 8 made of a highly conductive material such as aluminum carries off an appreciable amount of the heat from the nettings 10b and particularly from the inner netting lltlb having a rim portion directly contacting the flange of the burner body, whereby the inner netting ill is most effectively cooled and the flash back stability of the burner is appreciably improved. The heat conducted off in this manner is transmitted vfrom the reilector to the cool gas-air-mixture flowing into the burner by radiation and convection. Therefore the eilciency of the burner is not decreased by this heat llow from the nettings itlb to the burner body 8. It was found to be of importance that at least the inner netting llt) contacts the reilector on an area of appreciable size so that an intensive heat exchange may take place between such parts.

The flowing resistance of the outer diaphragm or delimitation of the burner, consisting of the wire nettings lil is relatively small as compared with the discharge surface of the burner, soV that a high percentage of primary combustion air is aspirated by the gas jet. Therefore, the combustible mixture hasa high oxygen content and will practically completely be combusted in the meshes of the outer netting lila, so that the full combustion energy will directly contribute to the heating of the outer netting lila. Consequently a relatively high eiliciency of the burner is obtained.

The described radiating burner is particularly suitable as a radiation heating element in drying ovens or grill ovens. For the last mentioned application of the radiating burner it is very important that the period for heating up the same is very short as compared with the treating period of the meat to be grilled, a high elliciency in operation being thereby obtained in addition to the above mentioned high thermal efllciency of the burner.

The nettings 10 might be different in size of mesh, whereby the coarser netting is preferably used for the outer enevelope lila. The wire nettings might also be replaced by other suitable gas pervious envelopes, for instance by porous, sintered layers or the like. Refractory nettings of suitable materials other than metals might as well be used.

In order to improve the Hash-back stability of the radiating burner more than two gas pervious envelopes might be provided which might be of the same or of diierent mesh size and material.

While the invention has been described and illustrated with reference to a specific embodiment thereof, it will be understood that other embodiments may he resorted to without departing from the invention. Therefore, the form of the invention set out above should be considered as illustrative and not as limiting the scope of the following claim.

What I claim is:

A tast starting radiating gas burner wherein the combustion of an explosive gas-air mixture heats an external diaphragm to incandescence, Hash-back is prevented, and the combustion zone is external of this diaphragm, comprising a mixing tube having an air inlet, a gas nozzle directed into said mixing tube for setting up a flow of an explosive gas-air mixture therethrough, a distributing cap on the end of said tube and having discharge openings therein, a burner body attached to said mixing tube and in communication with the said mixing tube through the cap, said body being cup-shaped of large diameter relative to said tube and cap and having a heat reflective inner surface, an outwardly projecting flange on the edge of said body, a diaphragm closing the cup-shaped body and defining together with said body a relatively cool and large fuel distributing chamber, said diaphragm including two slightly spaced gas pervious meshed grids, the edges of said grids being connected to said flange with the innermost grid engaging the entire diaphragm-facing ilange surface in efllcient heat conducting contact therewith, said diaphragm being outwardly convex for more efficient fuel distribution thereon from the relatively small distributing cap, said inner grid directly facing said cap so that the grid is cooled by the fuel as it llows from said cap into said body and prior to the combustion thereof outside of the outer grid, the openings of the grids being of substantially equal size of not more than one millimeter and said grids being juxtaposed with the strands of the inner grid traversing the openings of the outer grid to reilect heat back through said outer grid, the spacing and alignment of the grids, the heat conducting connection between the body ange and the inner grid, the heat rellection of the internal body wall and inner grid, and the cooling fuel ilow directly on the inner grid all cooperating to keep the inner grid relatively cool whereby combustion is restricted to the zone within the meshes and over the Outer face of said diaphragm and Hash-back is prevented.

References Cited in the file of this patent UNITED STATES PATENTS 824,361 Hudson June 26, 1906 6 Johnson Feb. 6, 1934 Smith Oct. 1, 1935 Vixler May 19, 1953 FOREIGN PATENTS Great Britain of 1913 France Apr. 13, 1921 Great Britain Oct. 17, 1938 

